The present invention relates to a flow control device of a helically-shaped intake port of an internal combustion engine.
A helically-shaped intake port normally comprises a helical portion formed around the intake valve of an engine, and a substantially straight inlet passage portion tangentially connected to the helical portion. However, if such a helically-shaped intake port is so formed that a strong swirl motion is created in the combustion chamber of an engine when the engine is operating at a low speed under a light load, that is when the amount of air fed into the cylinder of the engine is small, since air flowing within the helically-shaped intake port is subjected to a great flow resistance, a problem occurs in that the volumetric efficiency is reduced when the engine is operating at a high speed under a heavy load, that is, when the amount of air fed into the cylinder of the engine is large.
In order to eliminate such a problem, the inventor has proposed a flow control device in which a bypass passage, branched off from the inlet passage portion and connected to the helix terminating portion of the helical portion, is formed in the cylinder head of an engine. A normally closed type flow control valve, actuated by an actuator, is arranged in the bypass passage and opened under the operation of the actuator when the amount of air fed into the cylinder of the engine is larger than a predetermined amount. In this flow control device, when the amount of air fed into the cylinder of the engine is large, that is, when the engine is operating under a heavy load at a high speed, a part of the air introduced into the inlet passage portion is fed into the helical portion of the helically-shaped intake port via the bypass passage. This reduces the flow resistance of the helically-shaped intake port enabling high volumetric efficiency. However, in such a flow control device, in order to actually obtain a high volumetric efficiency and create a strong swirl motion, it is necessary to retain the flow control valve precisely at the full open position and at the completely closed position. Nevertheless, this flow control device is just the embodiment of the basic principle of operation and thus is not constructed so that the flow control valve can be retained precisely at the fully open position and the completely closed position. Therefore, in the flow control device, it is difficult to actually obtain a high volumetric efficiency and create a strong swirl motion.